1. Field of the Invention
The present invention provides a method for controlling the profile of a metal strip such as a steel or aluminum sheet or plate during its rolling.
2. Description of the Prior Art
In rolling a sheet material (workpiece) using equipment having a capability of shifting the positions of working rolls in the axial direction, the following two methods have been proposed for preventing the development of an abnormal profile having a local projection (also referred to as a "high spot") in the work resulting from local wear in the working rolls:
(1) A sheet profile meter is disposed on the delivery end of the final stand in a rolling mill and if, on the basis of the information provided by this profile meter, a sign of local wear in the working rolls or a high spot in the rolled sheet that has resulted from local wear is detected, the pair of working rolls are displaced axially by an amount sufficient to eliminate or reduce the high spot (see, for example, Japanese Patent Publication No. 38842/1984). This method may be implemented with a roll mill having axial shiftable working rolls (see, for example, U.S. Pat. No. 2,047,833, the substance of which is incorporated by reference as if fully set forth herein)
(2) The profiles of the working rolls are first determined and the development of a high spot is prevented by changing axially the relative position of the pass line of the work with respect to the working rolls acting thereon (this practice is conventionally referred to as off-center rolling) such that the rolls will wear uniformly in the axial direction (see, for example, Japanese Patent Laid-Open Publication No. 68662/1978).
The two above-described methods are similar to each other in that they use the profiles of working rolls as a primary control parameter and, by changing the positions of these rolls with respect to the work sheet, they reduce any local wear in a specific area of the rolls in a sufficient amount to provide smooth roll profiles so as to prevent the development of a high spot. The essence of each method is to change the positions of the pair of working rolls relative to the work, namely the positions at which the work contacts the upper and working rolls. In this respect, the two conventional methods differ from the method of the present invention which changes the positions of the upper and lower working rolls individually and in opposite directions.